History of Atomic Theory

Vocabulary flashcards covering key terms and concepts from the history of atomic theory as presented in the lecture notes.

Aristotle's Four Elements

Earth, air (wind), fire, and water, as the fundamental constituents of matter according to Aristotle.

Atomism

The theory that matter is composed of tiny indivisible particles called atoms moving in a void.

Democritus

Ancient Greek philosopher who argued for atomism and that atoms rearrange to form the changing world.

Paramenides

Philosopher who argued that change is an illusion because something cannot come from nothing.

Atom

The fundamental, indivisible unit of matter in early atomic theory; Greek ‘atomos’ meaning uncuttable.

Void

Empty space through which atoms were thought to move in early atomism.

Atomós (Greek)

Greek for ‘indivisible,’ the origin of the word atom.

Robert Boyle

17th-century chemist who promoted the New Philosophy, studied gases, built vacuum pumps, and advanced corpuscularian ideas.

Corpuscularism

Theory that matter is made of tiny particles called corpuscles; precursor to modern atomic theory.

The Sceptical Chymist

Boyle’s 1661 work advocating a corpuscularian view of elements and compounds.

Lavoisier

French chemist who formulated the Law of Conservation of Mass.

Law of Conservation of Mass

Mass is neither created nor destroyed in ordinary chemical reactions.

Proust

French chemist who proposed the Law of Definite Proportions.

Law of Definite Proportions

A given compound contains elements in fixed, definite mass ratios.

Dalton

English chemist who developed atomic theory and the Law of Multiple Proportions.

Law of Multiple Proportions

When elements form compounds, the masses of one element combining with a fixed mass of the other are in small whole-number ratios.

Dalton's Atomic Theory

Elements are made of atoms; atoms of a given element are identical; compounds form by atom rearrangement; chemical reactions do not change atoms themselves.

First Table of Atomic Masses

Dalton’s early attempt to quantify atomic masses by comparison to a standard.

Avogadro's Hypothesis

Equal volumes of gases at the same temperature and pressure contain the same number of particles.

Gay-Lussac (Combining Volumes)

Gas-volume relationships supporting Avogadro’s idea; volumes of reacting gases combine in simple ratios.

J.J. Thomson

Physicist who discovered the electron and proposed the plum pudding model of the atom.

Electron

Subatomic particle with negative charge; discovered by Thomson.

e/m ratio

Charge-to-mass ratio of the electron, ≈ -1.76 × 10^8 C/g.

Robert Millikan

Experimentally determined the elementary electric charge using oil drops; helped determine electron mass.

Plum Pudding Model

Thomson’s atomic model with a positively charged ‘pudding’ containing embedded electrons.

Rutherford

Physicist who showed through the gold foil experiment that atoms have a small, dense nucleus.

Nuclear Atom

Atomic model with a central nucleus containing protons and neutrons and electrons in surrounding space.

Proton

Positively charged subatomic particle in the nucleus.

Neutron

Electrically neutral subatomic particle in the nucleus, discovered by Chadwick.

Isotopes

Atoms of the same element with the same number of protons but different numbers of neutrons.

Atomic Number (Z)

Number of protons in the nucleus; identifies the element.

Mass Number (A)

Total number of protons and neutrons in the nucleus.

Atomic Symbol Reading

Interpreting Z (protons) and A (protons+neutrons); neutral atoms have equal numbers of protons and electrons.

Planck

Physicist who introduced energy quantization and Planck’s constant.

Quantum

Discrete units of energy; energy exhibits particle-like and wave-like properties.

Planck's Constant

h; relates energy of a quantum to its frequency via E = hν.

Photoelectric Effect

Phenomenon explained by Einstein: light consists of photons; emission of electrons depends on photon energy.

Photon

Quantum of light; particle-like unit with energy E = hν.

Hydrogen Emission Spectrum

Discrete wavelengths emitted by excited hydrogen, forming a line spectrum and indicating quantized energy levels.

Bohr Model

Quantum model for hydrogen placing the electron in fixed orbits around the nucleus.

Quantum Mechanical Model

Modern atomic model describing electrons with wave functions and probabilities rather than fixed orbits.

Wave Functions

Mathematical descriptions of electron position and movement; basis of the QM model.

Uncertainty Principle

Principle by Heisenberg: precise position measurement limits the precision of momentum determination.

Heisenberg

Physicist who formulated the Uncertainty Principle and helped develop quantum mechanics.

de Broglie

Physicist who proposed wave-particle duality for matter.

Schrödinger

Physicist who developed wave mechanics and the Schrödinger equation.

Chadwick

Physicist who discovered the neutron in 1932 by studying radiation from bombarded Be.

Neutron Discovery (1932)

Identification of a neutral, massive subatomic particle in the nucleus.